1. Field of the Invention
The invention relates to gas masks and filter canisters etherefor. In one aspect, the invention relates to a filter canister having a profile that conforms to the curvature of the wearer's face. In another aspect, the invention relates to a gas mask with a mask housing and a filter cartridge that conforms to the face of the wearer. In another of its aspects, the invention relates to a low profile filter canister that has a relatively high flow rate and relatively low flow resistance. In yet another of its aspects, the invention relates to an axial flow filter canister that has a relatively low flow resistance.
2. Description of the Related Art
PCT International Publication No. WO 01/78839, published Oct. 25, 2001, discloses a bayonet-type connector for connecting a removable filter to a gas mask. A filter canister comprising a hollow container having an oval shape is also disclosed, with parallel planar top and mounting surfaces separated by a perimeter wall. The canister is mounted to the mask with a twist and lock mechanism for quick change of spent canisters. A secondary filter for treating toxic industrial materials is disclosed for adding to the primary canister as necessary by a twist and lock mechanism.
U.S. Pat. No. 5,019,311 to Koslow, issued May 28, 1991, discloses a process for producing a composite material having carbon particles combined with binder particles which, through heat and pressure, are formed into a substantially uniform, stabilized mixture which can retain a preselected shape.
Conventional replaceable circular or elliptical gas mask filters with parallel planar top and mounting surfaces can be mounted to one or to both sides of the mask and extend laterally outwardly of the mask. Such filters typically comprise a folded paper or fabric particulate filter and a granulated carbon adsorption filter. In order to maximize the density of the carbon granules and avoid introducing flow channels through the adsorption filter, the granulated carbon is typically placed in the filter canister through a process of “snow storm filling” the granulated carbon into the filter in such a way that the density of the granules is maximized. This process requires that the top and mounting surfaces be flat.
Laterally-mounted filters with flat top and mounting surfaces extend outwardly of the wearer's face, and can interfere with the wearer's vision and activities (e.g. sighting a firearm), or contact objects in close proximity to the wearer, potentially damaging the filter and rendering it inoperative, and injuring the wearer. Because the auxiliary filter further extends outwardly of the mask, the use of an auxiliary filter can exacerbate the problems inherent with the outwardly extending primary filter.
Filters having a curved section to conform closely to the curvature of the wearer's face can mitigate many of the problems associated with conventional filters having flat top and mounting surfaces. However, the curvature of the filter interferes with the conventional “snow storm filling” method of placing the carbon filter granules in the filter canister, and can prevent the granules from assuming a sufficient density. As well, the curvature of the filter canister can cause unacceptable variations in the thickness of the carbon layer, leading to insufficient protection of the wearer.
A mask with dual filter units shaped to conform to the shape of the face is disclosed in U.S. Pat. No. 5,078,132 and U.S. Pat. No. 6,176,239. The filter units are of a non-circular shape and appear to be molded of a particulate filter material with a binder.